Roy Williams will serve a one-game suspension. Dallas Morning News has a statement from the NFL that reads:
Commissioner Goodell has denied the appeal of the one-game suspension of Roy Williams. The ‘horse collar’ tackling technique is prohibited because the Competition Committee and the clubs have determined that it presents an unacceptable risk to player safety. Rules that protect and advance player safety must be enforced in a way that will deter violations and prevent injuries from occurring.